This invention relates to apparatus for driving selectively one of a plurality of thread take-up arms of a multicolor embroidery machine head, wherein the head also contains one thread supply and one needle assembly for each thread take-up arm, and is constructed so that only one color stitching set, comprising a thread take-up arm, a needle assembly, and a thread supply can be driven at a time. The thread passes through a hole in the thread take-up arm and the needle in the needle assembly. During operation the needle assembly pierces a workpiece with a threaded needle, a stitch is formed, and the corresponding thread take-up arm pulls upwardly only that thread stitched to tighten the stitch while all other thread take-up arms, needle assemblies, and threads remain stationary.
The invention also relates to an apparatus for driving selectively one of a plurality of thread take-up arms of a multicolor embroidery machine head wherein a plurality of heads having the same construction are assembled to form a multihead embroidery machine, wherein each head is capable of shifting from a first selected color stitching set to a second selected color stitching set under computer control, thereby changing the color thread being stitched. Such multihead embroidery machines form stitches in the workpieces secured to a frame by moving the frame, under computer control, about the stitching points while the needle assemblies reciprocate vertically.
Single head embroidery sewing machines using only one thread take-up arm and only one needle driven from a common power source are old in the art. It is also known to construct a machine that has a plurality of embroidery machine heads with a single thread take-up arm and a single needle for stitching one color thread at a time, as is shown in Schmedding et al. U.S. Pat. No. 3,783,811, and Bohman et al. U.S. Pat. No. 2,091,727.
Individual embroidery machines having multiple needles on a single head are also known. Such needles may be arranged on a turret so that the color change is effected by manual rotation of the turret as shown in Schwarzmann U.S. Pat. No. 1,234,398 and Chambers U.S. Pat. No. 3,118,403. Both Schwarzmann and Chambers use tension devices to control thread advance, but neither show any thread take-up mechanism. Other multicolor embroidery machines have the several needles mounted in and arranged along either a curved or a flat plate, where change is effected by moving the plate, as shown in Sacchetti U.S. Pat. No. 4,075,958 and Bolldorf U.S. Pat. No. 4,276,838.
Multihead embroidery machines which also have some color change capability are also known in the art as shown in Desprez et al. U.S. Pat. No. 4,295,433, and as are available from Tajima Industries Ltd., Nagoya, Japan (for example Model TMB 112).
In one known multihead color change embroidery machine each head has only one thread take-up mechanism through which all threads pass. See for example Sacchetti U.S. Pat. No. 4,075,958. In a second known multihead embroidery machine, as shown in Desprez et al. U.S. Pat. No. 4,295,433, each head has one thread take-up mechanism which has several holes so that only one thread passes through each hole. The problem inherent in these machines is the constant motion of the take-up mechanism causes all of threads to move, including the threads not being stitched. This results in structural weakening of the threads, pulling the threads out of the needle, or tangling the threads in the apparatus, requiring shutdown of the embroidery machine for rethreading or repair.
Multihead machines with color change capability are known wherein there is a separate take-up lever associated with each color thread and needle. The thread take-up arms shown in the Tajima Industries Ltd. machines have a long connecting shaft or a series of axially aligned shafts directly connecting take-up arm mechanisms on adjacent heads together. The thread take-up levers shown in Bolldorf et al. U.S. Pat. No. 4,369,721 must rely on an elaborate geared apparatus involving a drive shaft, a thread take-up lever, a coupling member attached to the drive shaft, a coupling clutch to engage the drive shaft to the thread take-up lever and operate the thread take-up lever, such that the thread levers remain fixed relative to the stitching point, and a control shaft with a coupling and decoupling member for each thread lever for selecting which lever is operative, independent of needle movement.
One problem with conventional multihead and multicolor embroidery machines, as shown in the Tajima machine, is that the thread take-up mechanisms, mounted on sliding carriages, are connected together by either one long shaft that passes through every thread take-up mechanism and carriage and extends the length of the multihead machine, or by a series of shafts connecting adjacent thread take-up mechanisms and carriages. A second problem is that the movement of the thread take-up mechanisms on every head is dependent upon a single cam, located at one end of the machine. The cam picks up its motion directly from the main drive motor and causes the connecting shaft or shafts to rotate one-half or three-quarters turn about its longitudinal axis to move the thread take-up mechanism up and down.
These problems require that every head be aligned perfectly and oriented identically for the multihead machine to operate in both the stitching and the color change functions. Otherwise, rotation of the shaft to operate the thread take-up mechanism will bind rather than move the several misaligned thread take-up mechanisms. Similarly, the carriages on the several heads will not slide smoothly during the color change operation.
Further, a slight misalignment or breakdown of one head requires that the entire multihead machine be shutdown while the repair is made. Thus it is difficult to transport or move such a machine, and maintenance can be a costly necessity. An additional problem is that heads located furthest from the drive cam may not move in synchrony with the closer heads because of mechanical flexure inherent in the one or more connecting shafts, thus creating distorted and non-uniform patterns on the several workpieces.
The problem with the Bolldorf multihead and multicolor embroidery machines is that the coupling and decoupling means for driving the plurality of thread take-up arms are mechanically complicated. The multiplicity of gears are subject to wear and slippage over time, and the thread take-up arms are subject to backlash movements during decoupling. Consequently, the threads are subjected to variable tensions that weaken the thread and result in uneven stitches in the workpieces.
It is therefore an object of this invention to provide a multihead embroidery machine with automatic color change capability wherein each head has a plurality of color stitching sets of associated thread take-up arm, needle assembly, and color thread, and only one color stitching set is operative for stitching the associated color thread while the remaining sets are inactive and held motionless, and the color thread to be stitched is changed on each head by changing the color stitching set in stitching position.
It is another object of this invention to provide a thread take-up arm drive means, powered by a drive shaft, that reciprocates vertically under a biasing force exerted by a leaf spring that controls the motion of the thread take-up arm drive means.
It is another object of the invention to provide a multihead embroidery machine where each head has only one drive shaft for operating the thread take-up arm drive means and the needle assembly drive means, for driving only one of a plurality of color stitching sets at a time without any mechanical connection between thread take-up arms or needle assemblies of adjacent heads, and for providing an improved thread take-up arm motion and stitching action.
It is another object of the invention to provide a computer controlled color change apparatus for a multihead embroidery machine wherein a plurality of thread take-up arms are fixed in relation to a corresponding plurality of needle assemblies, both the thread take-up arms and the needles are mounted on a carriage, the movement of the carriage is controlled by a step motor that operates a horizontal gear rack affixed to the carriage to select and engage one thread take-up arm and one needle assembly to their respective drive means, the drive means being connected to the one drive shaft, and the computer controlling the drive means and the step motor associated with each head simultaneously so that the color change occurs on each head smoothly independently, and substantially simultaneously.